System and method for limiting vibration in an apparatus during a loss of power

ABSTRACT

An apparatus comprising a frame; a member movable relative to said frame; a damping device interconnected between the frame and the movable member; a controller for activating said damper to generate a damping condition at a predetermined member operating condition; and system for activating the damping device at a predetermined operating condition of the moving member during a loss of power to the apparatus. The damping device may comprise a field controllable damper that includes a volume of field controllable fluid, which may in turn comprise magnetorheological fluid for example. The rheology of the field controllable fluid is effected during the application of said field.

FIELD OF THE INVENTION

The invention relates to an apparatus that includes a device forproviding the required damping, resistance and motion control to theapparatus where the device is actuated by a signal, and morespecifically the invention relates to a system and method for limitingvibration in an apparatus that employs a signal actuated damper during aloss of power to the apparatus.

BACKGROUND OF THE INVENTION

One class of well-known dampers and shock-absorbers uses a volume ofhydraulic fluid as the working medium to create damping forces tocontrol or minimize shock and/or vibration. Typically, the dampingforces are generated by pressures resisting movement between operativecomponents of the damper or shock absorber.

Another class of devices employed to minimize shock and/or vibrationcomprises devices that include a field controllable material such as amagnetorheological (MR) medium which may comprise MR fluid or MR powder.Such devices referred to as “MR devices” may be of the “rotary-acting”or “linear-acting” variety. Known MR devices include linear dampers,rotary brakes, and rotary clutches for example. Each MR device employsan MR medium comprised generally of soft-magnetic particles dispersedwithin a carrier. Typical particles include carbonyl iron, and the like,having various shapes, but which are preferably spherical and have meandiameters of between about 0.1 μm to about 500 μm. The carrier is mostfrequently a fluid among the group of fluids including low viscosityhydraulic oils, and the like. In operation, these MR fluids exhibit athickening behavior (a rheology change) upon being exposed to a magneticfield. The higher the magnetic field strength in the fluid, the higherthe damping/restraining force or torque that can be achieved within theMR device. The magnetic field is generated by supplying a current to acoil that is located proximate a pole piece

FIG. 1 illustrates an exemplary MR damper of the type disclosed in U.S.Pat. Nos. 6,151,930 and 5,284,330 commonly assigned to the assignee ofthe present invention, Lord Corporation of Erie, Pa. the disclosures ofwhich are incorporated herein by specific reference. Damper 10 may beused in a variety of applications. For example, a plurality of dampersmay be used to support an engine on a vehicle frame or to suspend a drumin a washing machine cabinet or housing. The damper 10 of FIG. 1includes cylindrical housing 12 that defines housing chamber 14 andpiston member 16 disposed in the chamber and adapted to be translatedlinearly along axis 17 through the housing chamber. An attachment stem28 is made integral with one end of the housing 12 in a conventionalmanner and the free end of the stem is in turn fixed to a frame such asthe frame of a machine or engine by a conventional connection membersuch as a bolt for example.

The piston body 18 and the housing wall 20 are made of a magneticallypermeable material such as a soft magnetic steel for example and thepiston body and housing comprise pole pieces that define the path ofmagnetic field 22 represented in dashed font in FIG. 1. The piston bodyincludes a piston rod 32 that is securedly fixed to the piston, and thefree end of the rod is in turn fixed in a conventional manner proximatethe member, device or system that is the primary source of vibratorydisplacement such as an engine or an enclosure for a washing machinedrum for example.

In the exemplary MR damper 10 of FIG. 1, a volume of a fieldcontrollable medium such as a magnetorheological medium is contained inan absorbent matrix 30 which is wrapped around the piston body 18. Theabsorbent matrix may include polyurethane foam for example. In analternate embodiment, illustrated in incorporated by reference U.S. Pat.No. 5,284,330 the field controllable material is not retained in anabsorbent matrix. A substantial portion of the housing chamber is filledwith a volume of the field controllable material and during operationthe field controllable material is displaced from one end of chamber 14to the opposite end of chamber 14 as it is entrained in a gap betweenthe piston body and housing wall during axial displacement of the pistonthrough the housing chamber.

A magnetic field generating means 24 in the form of a coil is mounted onthe piston body 18 to be movable with the piston as it isreciprocatingly displaced axially through the housing 14. The fieldgenerating means alters the rheology of the field responsive medium inproportion to the strength of the field. Wires 26 connect the coilcomprising the field generating means to a controller, not shown inFIG. 1. The controller is disclosed schematically in FIGS. 3 a and 3 band the controller will be described in greater detail hereinafter.

During operation of damper 10 the field controllable medium becomesincreasingly viscous with increasing field strength and provides a shearforce to resist relative movement between housing and piston members 12and 16. When the pole pieces are energized by magnetic field 22 thecontrollable fluid changes rheology in the matrix 30 located between themovable member 18 and the housing 12. In use, the circumferentiallyextending coil 24 generates a magnetic field 22 that acts on the polepieces 18 and 20 and the field controllable medium contained by thematrix 30. The coil generates a magnetic field in response to thecurrent supplied to the coil 24 by the controller. The resistive forceproduced by changing the field controllable medium's rheology can bevaried by changing the magnetic field strength which in turn iscontrolled by the amount of current supplied to the field generatingmeans 24 by the controller.

When the damper is used to suspend washing machine drums from thewashing machine cabinet, the magnitude of damping supplied is adjustedfor the different washing cycles. Turning now to FIG. 2 which is a graphrepresenting the transmitted washing machine forces during the range ofwashing machine drum spin speeds, the supplied damping is increasedbetween points A and B on FIG. 2 which defines a the range of speedsthat occur during machine resonance. For example, the washing machinerepresented by exemplary FIG. 2 experiences resonance as the drum passesthrough the speed range between minimum and maximum spin speed limitpoints A and B which may be 100 and 200 rpm for example. Resonanceoccurs during periods of machine drum acceleration and deceleration whenthe drum is spinning in the speed range between threshold points A andB. The supplied damping is reduced outside the spin speed range betweenpoints A and B.

The adjustable damping provided to washing machines by damper 10 is aconsiderable improvement over the single constant damping supplied bypassive damping devices. If the damping was not supplied throughresonance as the washing machine rotated through the speeds that producea resonance condition, the produced vibratory forces could cause thewashing machine to “walk” from its operating location. Also, thevibratory forces could damage the machine.

During a loss of power to the washing machine or other apparatussupported by one or more dampers 10, the required current is notsupplied to the field generating means 24 to control damper 10. As aresult, the requisite damping forces can not be supplied by damper 10 tocontrol the vibration produced during resonance experienced as thewashing machine rotates through the spin speeds between points A and B.Thus the washing machine passes through resonance undamped which couldcause the washing machine to vibrate from its desired operating positionand the machine could be damaged.

The foregoing illustrates limitations known to exist in present dampingdevices and methods. Thus, it is apparent that it would be advantageousto provide an alternative system and method whereby vibration iscontrolled in the event there is a loss of power to an apparatus.Accordingly, a suitable alternative is provided including features morefully disclosed hereinafter.

SUMMARY OF THE INVENTION

The present invention provides a method and system for controllingvibration in an apparatus in the event there is a loss of power to theapparatus. The invention relates to an apparatus that includes a devicefor providing the required damping, resistance and motion control to theapparatus where the device is actuated by a signal, and morespecifically the invention relates to a system and method for limitingvibration in an apparatus that employs a signal actuated damper during aloss of power to the apparatus.

More specifically, the present invention comprises an apparatus, thatfurther comprises a frame; a member movable relative to said frame;damping means including a volume of a field controllable medium, thefield controllable damper being interconnected between the frame and themovable member; a controller for activating said field controllabledamper to generate a damping condition at a predetermined memberoperating condition; and means for limiting vibration in said apparatusduring a loss of power to the apparatus.

Although the means for limiting vibration is described as a fieldcontrollable damper, it should be understood that the device forlimiting vibration may be any suitable damping device that is actuatedby an electrical signal.

The means for limiting vibration may comprise the combination of asecondary controller and a storage device such as a battery orcapacitor. Alternatively the secondary controller may be combined with agenerator or a DC motor. The secondary controller may also be combinedwith a magnet attached to the damper and a coil where current is inducedin the coil as the magnet is displaced by the damper. In eachcombination the battery, capacitor, generator, DC motor or magnet/coilproduces the supplemental power required to activate the secondarycontroller and dampers as required as the apparatus spins down tothereby limit vibration in the apparatus.

Also, the means for limiting vibration may comprise a brake that ismoved into engagement with the movable member when the power is lost bythe apparatus. Such a brake may include a biasing member such as aspring for biasing a contact member toward the movable member and asolenoid for maintaining the contact member away from the movablemember. During periods where power is being supplied to the apparatusthe solenoid is activated by the controller to maintain the contactmember away from the movable member. When power is lost, the solenoid isdeactivated and the biasing member moves the contact member into brakingengagement with the movable member.

The above-mentioned and further features, advantages, andcharacteristics of the present invention will become apparent from theaccompanying descriptions of the preferred embodiments and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which form a part of the specification,illustrate several key embodiments of the present invention. Thedrawings and description together, serve to fully explain the invention.

FIG. 1 is a longitudinal cross-section of a controllable linear damper.

FIG. 2 is a graph of transmitted forces from a washing machine tubduring a spin cycle.

FIG. 3 a is a front sectional view of a front loading washing machineincluding field controllable dampers and first and second alternateembodiment means for limiting vibration during loss of power to thewashing machine.

FIG. 3 b is a front sectional view of a front loading washing machineincluding field controllable dampers and third, fourth and fifthalternate embodiment means for limiting vibration during loss of powerto the washing machine.

FIG. 4 is a side sectional view of a top loading washing machineincluding field controllable dampers with integrated springs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Most generally, the present invention is a system and method forlimiting vibration in an apparatus during a loss of power. The apparatusmay include, but shall not be limited to a washing machine for example.The device for limiting vibration in such method and system may compriseany suitable vibration control device that is actuated by a signal. Thevibration control device may further comprise a field controllabledamper like damper 10 described hereinabove where vibration control isproduced by supplying a signal to the device to effect the rheology ofthe volume of the field controllable medium housed in the damper. Inorder to describe a preferred embodiments of the present invention, asthe description proceeds the system and method of the present inventionwill include the field controllable damper 10

Referring to the drawing FIGS. 3 a and 3 b that disclose the fivepreferred embodiments of the invention, it should be noted that thefirst and second embodiments are illustrated schematically on FIG. 3 aand the third, fourth and fifth embodiments of the invention areillustrated on FIG. 3 b. Multiple embodiments of the systems forlimiting vibration in an apparatus when power is lost are disclosed onthe same drawing figures to limit the number of figures included in thespecification. The embodiments are specific and discrete systems asdisclosed in accordance with the following description and moreover asidentified and referred to separately as systems 130 a, 130 b, 130 c,130 d and 130 e hereinafter.

Now referring to the drawings wherein like numerals denote like items,FIG. 3 a is a front sectional view of apparatus 100 a that comprises thesystem 102 of the present invention for controlling the dampers 10 a ofapparatus 100 a in the event electrical power supply to apparatus 100 ais lost. The first and second embodiment systems for limiting vibrationwhen power is lost are identified in FIG. 3 a as 130 a and 130 brespectively. For purposes of describing the preferred embodiments ofthe invention, the apparatus 100 a is a front loading clothes washingmachine. However it should be understood that the apparatus may be anyelectrically powered apparatus with damping that is controlled by one ormore field controllable dampers. More specifically, in addition to thefront loading clothes washing machine 100 a the apparatus may includetop loading washing machine 100 b shown in sectional schematic view ofFIG. 4 or a centrifuge (not shown). The systems and methods forcontrolling vibration operate the same on different apparatus so that asthe description proceeds the structure and functionality of the fivealternate embodiment systems will be described in use with the frontloading machine 100 a.

Returning now to the clothes washing machine illustrated in FIGS. 3 aand 3 b, the washing machine 100 a comprises a housing 102 that definesa chamber 104 with controllable dampers 10 a, such as those described inreference to FIG. 1, mounted in the apparatus 100 a as components of thesuspension and damping system. The field controllable dampers associatedwith top loading machine 100 b are identified in FIG. 4 as 10 b. Thefront loading machine 100 a has a horizontally-mounted drum 106including a rotational portion 108 rotationally fixed and drivablerelative to drum 106 by a conventional motor 112 and belt 114 system.The motor may be any conventional motor such as any AC or DC typeelectric motor. The motor is supported in a conventional manner by thehousing 102 using the required brackets or other suitable connectionmembers (not shown). The drum 106 (and rotational portion 108) areflexibly suspended relative to a housing or cabinet 102 by flexiblesprings 116, such as coil springs for example. Dampers 10 a, of the typepreviously described hereinabove provide control of radial vibrations ofthe drum 106.

The dampers 10 are connected to master controller 120 in signalreceiving relation to the controller. The controller 120, which may beany suitable microprocessor based controller, is in signal receivingrelation with sensor 122 which may be a speed sensor for monitoring therotational velocity of drum 108 or an accelerometer that monitors drumvibration. The sensor is fixedly mounted on the housing drum 106, butmay be fixed in any suitable location. For example, alternatively, theaccelerometer may be fixed to the housing 102 to measure the housingvibration.

During use, when power is supplied continuously to the washing machine100 a, and the drum 108 is spinning with a rotational velocity or drumspin speed that is within a range of speeds predetermined to coincidewith a resonance condition in the drum, (for example the range betweenpoints A and B in FIG. 2) a damper activating signal, in the form of acurrent is sent from the master controller 120 to the dampers 10 a inthe manner represented schematically in FIG. 3 a. The resonancecondition typically occurs during the machine spin cycle. The currentsignal sent by controller 120 to the dampers changes the rheology of thefield controllable material. As the viscosity of the material isincreased the dampers 10 a provide the damping required to absorb thevibratory loads present during the resonance condition. At predeterminedintervals, the sensor 122 delivers signals indicating the measuredrotational velocity of the drum 108 to the master controller 120 and thecontroller logic determines when the speed of the drum is outside theresonance spin speed limits. When the speed is outside of the spin speedrange defined between points A and B, the controller stops sending thecurrent signal to the dampers and the damping provided by dampers 10 ais reduced.

The apparatus 100 a also includes a first embodiment means for limitingvibration in the apparatus 100 a in the event that there is a loss ofpower to the apparatus, and such first embodiment means is designatedgenerally at 130 a in FIG. 3 a. When power is lost by the apparatus, thecontroller 120 also loses power and cannot transmit signals to dampers10 a as required. The first embodiment means 130 a is comprised of astorage means such as a battery or other storage cell 132 and asecondary controller 134. The secondary controller controls the dampingsupplied by field controllable dampers 10 a during a loss of power tothe apparatus 100 a and the secondary controller may comprise anysuitable microprocessor based controller. As shown in FIG. 3 a, thesecondary controller is electrically connected to the storage means insignal receiving relation therewith. The secondary controller 134 isalso in signal receiving relation with main controller 120 and is insignal transmitting relation with dampers 10 a of apparatus 100 a.

In use, the main controller 120 transmits a voltage signal to thesecondary controller at predetermined intervals to indicate that poweris being supplied to the apparatus. The signal may be a 5V or 12V signalfor example. If during at least one interval the signal is nottransmitted to the secondary controller, the secondary controller logicdetermines that the main power supply to the apparatus has been lost.The secondary controller 134 immediately begins to draw power from thebattery 132 to power up controller 134. Signals are sent from sensor 122through the controller 120 to the secondary controller. After power islost by apparatus 100 a the rotational speed of the drum naturallystarts to decrease. Assuming the rotational speed of the drum is aboveupper limit B of FIG. 2 when the power is lost, when the sensedrotational velocity of the drum reaches the predetermined upperresonance limit, B, in FIG. 2 a current signal is sent from secondarycontroller 134 to dampers 10 a to provide the damping required to offsetthe vibratory forces generated during the resonance condition. In thisway, if power is lost, the apparatus 100 a will not be damaged and willnot “walk” from it desired operating location.

Once the speed of the drum is sensed to be below the spin speedrepresented by point A in FIG. 2, the secondary controller stops sendingcurrent signals to dampers 10 a. Soon thereafter, the drum 108 comes toa stop. If the drum is rotating at a speed that is below resonance lowerspeed limit A when the power is lost, the battery will continue tosupply power to the secondary controller 134 and no signal will be sentto dampers 10. The battery may have enough storage capacity to power thesystem 130 a for a period of about 5-10 seconds which is about theperiod required to rotate the drum down to a stop from any operatingspin speed.

If the motor 112 is a conventional direct current (DC) type motor, thekinetic energy of the drum 108 is converted to electrical energy by theDC motor and the electrical energy is available at the terminals of theDC motor. In an alternate embodiment of the invention identified at 130b in FIG. 3 a, during normal use of apparatus 100 a the storage means132 may receive a charge from the motor 112. The storage means may be abattery or conventional capacitor plate. Alternatively, the storagemeans may be a bank of batteries or capacitor plates. The motor iselectrically connected to the main controller in signal transmittingrelation with the controller. The electrical connection is representedin dashed font connection 136. In the alternate embodiment means forcontrolling vibration during loss of power 130 b, the capacitor (orbattery) is continuously charged during operation of apparatus 100 a.The storage device 132 receives the charging signal from the maincontroller as represented schematically in FIG. 3 a.

When power is lost by the apparatus 100 a, the secondary controller 134immediately begins to draw power from the storage device 132. Thecapacitive energy is released to the controller 134 and dampers 10 a asrequired in the manner previously described in conjunction with firstembodiment means 130 a until the drum comes to a stop.

Third, fourth and fifth embodiment means for activating dampers 10 andfail safe controller 134 during a loss of power to apparatus 100 a areillustrated in FIG. 3 b and are identified generally as 130 c, 130 d and130 e respectively. In third embodiment means 130 c, a conventionalgenerator 140 is located proximate spinning drum 108 and is connected tothe drum by a conventional belt 142 and in this way, the kinetic energyof the drum is converted to electrical energy by the generator as thedrum rotates.

Although the electrical generator means 140 is illustrated in FIG. 3 bas being located away from motor 112 and driven by separate drive belt142, it should be understood that the generator may be mechanicallyconnected to the rotating shaft 113 of motor 112 or to the motor drivebelt 114.

In use, when the apparatus 100 a loses power, as the drum 108 spinsdown, the generator continues to produce electrical power that issupplied directly to the secondary controller 134. If during the spindown the drum speed falls within the spin speed range between points Aand B of FIG. 2 the secondary controller supplies current signals todampers 10 a. The generator continues to produce electrical energy untilthe drum 108 stops rotating.

A fourth embodiment means for limiting vibration during a power loss isidentified at 130 d in FIG. 3 b. The fourth embodiment means comprisesan electromechanical brake. Shown schematically in FIG. 3 b, the brakecomprises a contact member 150 with a contact end 152 located proximatethe movable drum 108. The brake comprises a pair of spaced rigid plates154 a, 154 b. Plate 154 b is fixed and plate 154 a is movable linearlyrelative to plate 154 b. The ends of a conventional spring member 156such as a coil spring are connected to the plates and the spring memberserves to bias the plates apart. Solenoid member 158 has ends that areconnected to the plates 154 a and 154 b and the solenoid serves toovercome the outward bias of spring member 156. During the supply ofpower to apparatus 100 a an activating signal, in the form of a voltage,is sent to solenoid 158 from controller 120 and serves to maintain thesolenoid retracted. When the solenoid is retracted the braking end 152of contact member 150 is out of contact with the drum.

When power is lost, the solenoid activating signal is terminated, and asa result, the spring extends causing plate 154 a to move linearly awayfrom plate 154 b and thereby causing braking member end 152 to be movedinto braking contact with the rotating drum. The contact between member150 and drum 108 causes the drum to decelerate to a stop quickly. Brake130 d of the fourth embodiment means of the present invention isillustrated schematically for purposes of describing a fourth preferredembodiment of the invention however it should be understood that thebrake may assume a variety of configurations. In summary the brakecomprises a braking member and a means for maintaining the member awayfrom the rotating drum when power is supplied and for causing the memberto be moved into engagement with the drum when power to the apparatus islost.

The fifth embodiment means for limiting vibration during a power loss isidentified as 130 e in FIG. 3 b. The fifth embodiment system utilizesdamper motion to induce electric current in a coil located proximate thedamper. A conventional permanent magnet 160 is fixed to the exterior ofthe housing of dampers 10 a to be movable therewith. The coil ofconductive wire 162 is located proximate each magnet member and isstationary. As the damper is displaced linearly the damper induceselectric current in the coil in a conventional manner well known to oneskilled in the art. As shown in FIG. 3 b, each coil is located in signaltransmitting relation to the secondary controller 134.

When the power is supplied to apparatus 100, the current is induced incoil 162 as the dampers 10 are displaced linearly to offset vibration ofdrum 108. When the power is lost, the electric current is released todrive the secondary controller. The dampers 10 a are activated asrequired by current signals from the controller 134.

While several embodiments including the preferred embodiment of thepresent invention have been described in detail, various modifications,alterations, changes, and adaptations to the aforementioned may be madewithout departing from the spirit and scope of the present inventiondefined in the appended claims. It is intended that all suchmodifications, alterations, and changes be considered part of thepresent invention.

1. An apparatus, comprising: a) a frame; b) a member movable relative tosaid frame; c) damping means including a volume of a field controllablemedium, the field controllable damper interconnected between the frameand the movable member; d) a controller for activating said fieldcontrollable damper to generate a damping condition at a predeterminedmember operating condition; and e) means for activating said dampingmeans at a predetermined operating condition of the moving member duringa loss of power to the apparatus.
 2. The apparatus as claimed in claim 1wherein the device is a washing machine.
 3. The apparatus as claimed inclaim 2 wherein the device is a front loading washing machine.
 4. Theapparatus as claimed in claim 2 wherein the device is a top loadingwashing machine.
 5. The apparatus as claimed in claim 1 wherein thedevice is a centrifuge.
 6. The apparatus as claimed in claim 1 whereinthe field controllable medium is a magnetorheological medium.
 7. Theapparatus as claimed in claim 6 wherein the magnetorheological medium isa magnetorheological fluid.
 8. The apparatus as claimed in claim 6wherein the magnetorheological medium is a magnetorheological powder 9.The apparatus as claimed in claim 1 wherein the damping means is apiston-type damper.
 10. The apparatus as claimed in claim 1 wherein saidmeans for activating said damping means during a loss of power to theapparatus is comprised of a secondary controller and a storage device,said secondary controller being in signal receiving relation with thestorage device.
 11. The apparatus as claimed in claim 10 wherein saidstorage device is comprised of at least one battery.
 12. The apparatusas claimed in claim 10 wherein the storage device is comprised of atleast one capacitor.
 13. The apparatus as claimed in claim 1 whereinsaid means for activating said damping means during a loss of power tothe apparatus is comprised of a secondary controller and a means forgenerating a signal for activating the secondary controller and dampingmeans, said secondary controller being in signal receiving relation withthe signal generating means and being in signal transmitting relationwith the damping means.
 14. The apparatus as claimed in claim 13 whereinthe signal generating means is a storage device.
 15. The apparatus asclaimed in claim 14 wherein the storage device is a battery.
 16. Theapparatus as claimed in claim 14 wherein the storage device is acapacitor.
 17. The apparatus as claimed in claim 13 wherein the signalgenerating device is a generator.
 18. The apparatus as claimed in claim13 wherein the signal generating device is a DC motor.
 19. The apparatusas claimed in claim 13 wherein the signal generating device is comprisedof a magnet mounted on the damper and a coil proximate the coil.
 20. Anapparatus, comprising: a) a frame; b) a member movable relative to saidframe; c) damping means including a volume of a field controllablemedium, the field controllable damper interconnected between the frameand the movable member; d) a controller for activating said fieldcontrollable damper to generate a damping condition at a predeterminedmember operating condition; and e) a means for limiting vibration insaid apparatus during a loss of power to the apparatus.
 21. Theapparatus as claimed in claim 20 wherein the means for limitingvibration is comprised of a brake.
 22. (canceled)
 23. (canceled) 24.(canceled)
 25. The apparatus as claimed in claim 20 wherein said meansfor limiting vibration is comprised of a secondary controller in signalreceiving relation with a storage device, said secondary controllerbeing in signal transmitting relation with said damping means.
 26. Theapparatus as claimed in claim 20 wherein said means for limitingvibration is comprised of a secondary controller in signal receivingrelation with a DC motor, said secondary controller being in signaltransmitting relation with said damping means.
 27. The apparatus asclaimed in claim 20 wherein said means for limiting vibration iscomprised of a secondary controller in signal receiving relation with agenerator, said secondary controller being in signal transmittingrelation with said damping means.
 28. The apparatus as claimed in claim25 wherein the storage means is a battery.
 29. In an apparatuscomprising a frame; a movable member; a damping device including avolume of a field controllable medium, the field controllable damperinterconnected between the frame and the movable member; a controllerfor activating said field controllable damper to generate a dampingcondition at a predetermined member operating condition; and means foractivating the damping device at a predetermined operating condition ofthe moving member, the method comprising the steps of upon loss of powerto the apparatus, supplying an activating signal to the means foractivating the damping device and as required supplying activatingsignals to the damping device to change the rheology of the fieldcontrollable medium in the damping device.
 30. The method of claim 29further comprising the additional step of sending a signal from thecontroller to the damper activating means at predetermined intervals.31. In an apparatus comprising a frame; a movable member; a dampingdevice interconnected between the frame and the movable member wheresaid damping device is activated in response to a signal; a controllerfor supplying said signal to activate said damper to generate a dampingcondition at a predetermined member operating condition; and means foractivating the damping device at a predetermined operating condition ofthe moving member, the method comprising the steps of upon loss of powerto the apparatus, supplying an activating signal to the means foractivating the damping device and as required supplying activatingsignals to the damping device to provide the required damping to theapparatus.
 32. The method as claimed in claim 31 wherein the dampercomprises a field controllable damper comprising a volume of fieldcontrollable material, the method comprising the further step ofchanging the rheology of the field controllable medium in the dampingdevice when the signal is sent to the damping device.
 33. An apparatus,comprising: a) a frame; b) a member movable relative to said frame; c)damping means interconnected between the frame and the movable member,said damping means for supplying damping in response to an actuatingsignal; d) a controller for actuating said damper to generate a dampingcondition at a predetermined member operating condition; and e) meansfor limiting vibration in said apparatus during a loss of power to theapparatus.
 34. The apparatus as claimed in claim 33 wherein the dampingmeans is a field controllable damper, said damping means comprising avolume of a field controllable medium.
 35. The apparatus as claimed inclaim 34 wherein the field controllable medium is magnetorheologicalfluid.